Substantial effort and attention continues toward the development of newer and more sustainable energy supplies. The conservation of energy by increased energy efficiency remains crucial to the world's energy future. According to an October 2010 report from the U.S. Department of Energy, heating and cooling account for 56% of the energy use in a typical U.S. home. Along with improvements in the physical plant associated with home heating and cooling (e.g., improved insulation, higher efficiency furnaces), substantial increases in energy efficiency can be achieved by better control and regulation of home heating and cooling equipment. By activating heating, ventilation, and air conditioning (HVAC) equipment for judiciously selected time intervals and carefully chosen operating levels, substantial energy can be saved while at the same time keeping the living space suitably comfortable for its occupants.
In common air conditioning operation, a compressor compresses a refrigerant gas, which condenses in a condenser coil. The refrigerant passes through an expansion valve and into an evaporator coil that is cooled by the expanding and evaporating refrigerant. A fan is used to pass air over the cooled evaporator coil and move the cooled air into the indoor environment. As the air conditioning system operates, depending on the dew point of the air in the ducts and the temperature of the coil, condensation tends to form on the evaporator coil. After the air conditioning system ceases in normal operation the compressor and the fan are both turned off. However, if sufficient condensation has collected on the evaporator coil, additional cooling can be provided by continuing to operate the fan without the compressor. Of the two main energy-consuming parts of the system, the compressor generally consumes energy at a far greater rate than the fan. Accordingly, in some situations overall cooling costs and energy can be lowered by operating fan-only cooling for some time after each conventional air conditioning cycle.